Advances in set top boxes and associated software have enabled the emergence of new types of television viewing experiences. These viewing experiences include television applications such as enhanced TV (described below), games, tickers and other interactive and non-interactive applications. In each of these instances, there is often a need to synchronize the operation of the application and its associated events with an underlying related video program.
Enhanced TV (“ETV”) refers to the delivery of data to a client such as a set top box, a personal digital assistant, a video-enabled cellular phone, a television or other receiver in addition to conventional audio, video, teletext, and subtitle data that is delivered presently. This additional data may be used to enhance the viewing experience in many ways. It may be used to prompt the user to take certain actions, it may be used to place informational graphics on the television screen, or it may be used to create truly interactive programming, where the viewer has a great deal of control over what appears on the screen.
In a broadcast ETV system, a cable or satellite head end functions as a source. In this instance, the source is often a server or suite of servers that schedule and format enhancement data that sometimes needs to be synchronized with the conventional data. The enhancement data, in some instances, is then integrated into the audio and video data streams, and sent down to the end users' homes through a broadcast transmission system. The essential action of the source is the creation of a set of data for later distribution. Although the source is referred to in this document as a server, the source may not be a server in the strict sense. For instance, the source could be a software component that writes files to a disk for later broadcast or other distribution means, or annotates an MPEG file, or creates one or more proprietary files to be read by a transmission agent, such as a spooler.
On the end user side, there is generally a module in the television or set top box client in the viewer's home that interprets the ETV data. This module may carry out commands in the data itself, or it may launch a dedicated application, referred to as an enhancement, which may have its own methods of listening to and interpreting the ETV data.
In one system, ETV is an application running in a set-top box that is synchronized to the video appearing on the screen. For example, many companies have created ETV applications for game shows. When the on-screen contestants are asked a question during game play, the viewer is presented with the exact same question through an interface rendered by the set-top box. The ETV application generally allows user interaction, such as allowing the user to select an answer. This allows the viewer to play along with the video.
ETV and other television applications often need to perform certain events at the exact same time as on screen video events. Synchronizing the set-top box application with the on screen video is difficult for several reasons. Many set top boxes in particular are unable to read time code information normally associated with received video. Additionally, if video is received from a source that does not supply an embedded time code an alternative synchronization method must be used. Thus there is a need for a method of synchronizing an application with on screen video.